Apparatus and method for estimating channel

ABSTRACT

A method for transmitting a reference signal includes selecting one of a first initialization value and a second initialization value, generating selection instruction information corresponding to the selected initialization value, transmitting the selection instruction information to a mobile station, generating a reference signal based on the selected initialization value, and transmitting the generated reference signal to the mobile station. A method for estimating a channel includes receiving selection instruction information indicating a selection of at least one of a first initialization value and a second initialization value, receiving a first reference signal based on the selection instruction information, generating a second reference signal based on an initialization value indicated as being selected by the selection instruction information, and estimating a channel state by comparing the first reference signal with the second reference signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.13/670,915, filed Nov. 7, 2012, and claims priority from and the benefitunder 35 U.S.C. § 119(a) of Korean Patent Application No.10-2011-0115448, filed on Nov. 7, 2011, each of which is incorporatedherein by reference for all purposes.

BACKGROUND Field

The following description relates to a wireless communication system andmethod, and more particularly to an apparatus and method fortransmitting a reference signal in a wireless communication system, andan apparatus and method for estimating a channel by using the same.

Discussion of the Background

With technological progress of communication systems, consumers, such ascompanies and individuals, have used a wide variety of wirelessterminals.

In general mobile communication systems, as a high-speed andhigh-capacity communication system capable of transmitting and receivingvarious data, such as images and wireless data beyond voice-orientedservices, it may be desirable to develop a technology capable oftransmitting a large amount of data coming close to that of a wiredcommunication network. In addition, an appropriate error detectionscheme in which system performance can be improved by minimizinginformation loss and increasing system transmission efficiency, becomesan essential aspect in such a system.

Also, in many current communication systems, various reference signalsare used to provide information on a communication environment and thelike to a counterpart apparatus in uplink or downlink.

Also, multi-cell (or multi-point) cooperation has been introduced toincrease the performance and communication capacity of a wirelesscommunication system. The multi-cell (or multi-point) cooperation isalso referred to as cooperative multiple point transmission andreception (CoMP). The CoMP includes a beam avoidance technique in whichadjacent cells (or points) cooperatively mitigate interference caused toa user at a cell (or point) boundary, and a joint transmission techniquein which adjacent cells cooperatively transmit identical data, or thelike.

In a next-generation wireless communication system, such as those set bythe Institute of Electrical and Electronics Engineers (IEEE) or 3^(rd)Generation Partnership Project (3GPP), including IEEE 802.16m and 3GPPlong term evolution (LTE)-Advanced, an improvement in the performance ofusers who are located at a cell boundary and are subject to significantinterference from adjacent cells, is recognized as an importantrequirement.

SUMMARY

Exemplary embodiments of the prevent invention provide an apparatus anda method for generating a reference signal.

Additional features of the invention will be set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

Exemplary embodiments of the present invention provide a method fortransmitting a reference signal by a transmission point interlocked witha mobile station to the mobile station, the method including: selectingone of a first initialization value and a second initialization value;generating selection instruction information corresponding to theselected initialization value; transmitting the selection instructioninformation to the mobile station; generating a reference signal basedon the selected initialization value; and transmitting the generatedreference signal to the mobile station.

Exemplary embodiments of the present invention provide a method forestimating a channel by a mobile station interlocked with a transmissionpoint, the method including: receiving selection instruction informationindicating a selection of at least one of a first initialization valueand a second initialization value; receiving a first reference signalbased on the selection instruction information from the transmissionpoint; generating a second reference signal based on an initializationvalue indicated as being selected by the selection instructioninformation by using initialization value generation information; andestimating a channel state by comparing the first reference signal withthe second reference signal.

Exemplary embodiments of the present invention provide an apparatus totransmit a reference signal to be interlocked with a mobile station, themobile station including: a selection instruction information generatorto generate selection instruction information to indicate a selection ofat least one of a first initialization value and a second initializationvalue; a reference signal generator to generate a downlink referencesignal according to the selection instruction information; and atransmitter to transmit the selection instruction information and thegenerated reference signal to the more mobile station.

Exemplary embodiments of the present invention provides an apparatusinterlocked with a transmission point to estimate a channel state, theapparatus including: a reference signal receiver to receive a referencesignal from the transmission point; a selection instruction informationreceiver to receive, from the transmission point, selection instructioninformation to indicate a selection of at least one of a firstinitialization value and a second initialization value of a firstreference signal; a reference signal generator to generate a downlinkreference signal according to the selection instruction information; anda transmitter to transmit the selection instruction information and thegenerated reference signal to the more mobile station.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a schematic diagram illustrating a wireless communicationsystem according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating a macro cell and Remote Radio Heads(RRHs) forming a cooperative multiple point transmission and reception(CoMP) set and user equipments (UEs) performing transmission andreception with the cells and RRHs according to an exemplary embodimentof the present invention.

FIG. 3 is a diagram illustrating an environment facilitating atransmission of reference signals from Transmission Points (TPs) tomultiple mobile stations according to an exemplary embodiment of thepresent invention.

FIG. 4 is a flowchart illustrating a method for transmitting a referencesignal according to an exemplary embodiment of the present invention.

FIG. 5 is a flowchart showing a method for transmitting a referencesignal by a TP according to an exemplary embodiment of the presentinvention.

FIG. 6 is a flowchart showing a method for estimating a channel by amobile station according to an exemplary embodiment of the presentinvention.

FIG. 7 is a block diagram illustrating a configuration of an apparatusto generate and transmit a reference signal and information related tothe generation of the reference signal according to an exemplaryembodiment of the present invention.

FIG. 8 is a block diagram illustrating a configuration of an apparatusto estimate a channel according to an exemplary embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The invention is described more fully hereinafter with references to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. This invention may, however, be embodied in many differentforms and should not be construed as limited to the embodiments setforth herein. Rather, these exemplary embodiments are provided so thatthis disclosure is thorough, and will fully convey the scope of theinvention to those skilled in the art. It will be understood that forthe purposes of this disclosure, “at least one of X, Y, and Z” can beconstrued as X only, Y only, Z only, or any combination of two or moreitems X, Y, and Z (e.g., XYZ, XZ, XYY, YZ, ZZ). Throughout the drawingsand the detailed description, unless otherwise described, the samedrawing reference numerals are understood to refer to the same elements,features, and structures. The relative size and depiction of theseelements may be exaggerated for clarity, illustration, and convenience.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. Furthermore, the use of the terms a, an, etc. doesnot denote a limitation of quantity, but rather denotes the presence ofat least one of the referenced item. The use of the terms “first”,“second”, and the like does not imply any particular order, but they areincluded to identify individual elements. Moreover, the use of the termsfirst, second, etc. does not denote any order or importance, but ratherthe terms first, second, etc. are used to distinguish one element fromanother. It will be further understood that the terms “comprises” and/or“comprising”, or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof. Although some features may be described with respect toindividual exemplary embodiments, aspects need not be limited theretosuch that features from one or more exemplary embodiments may becombinable with other features from one or more exemplary embodiments.

FIG. 1 is a schematic diagram illustrating a wireless communicationsystem according to an exemplary embodiment of the present invention.

Referring to FIG. 1, a wireless communication system 10 is arranged toprovide various communication services, such as voice and packet data.The wireless communication system 10 includes at least one Base Station(BS) 11. The BS 11 may provide a communication service to a particulargeographical area or frequency domain, and may be called or referred toas a “site.” A site may be divided into multiple areas or cells,including a first cell 15 a, a second cell 15 b, and a third cell 15 c,which may also be called sectors, and the sectors or cells may havedifferent cell identifiers (IDs), respectively.

A Mobile Station (MS) or User Equipment (UE) 12 may be a stationarydevice or a device having mobility. The MS 12 may be called differentterms, such as a UE, a Mobile Terminal (MT), a user terminal (UT), asubscriber station (SS), a wireless device, a personal digital assistant(PDA), a wireless modem, and a handheld device.

The BS 11 may refer to a station communicating with the MS 12, and maybe called different terms, such as an evolved-NodeB (eNodeB), a BaseTransceiver System (BTS), an access point, a femto eNodeB, a Home eNodeB(HeNodeB), a relay, and a Remote Radio Head (RRH). One or more of thefirst cell 15 a, the second cell 15 b and the third cell 15 c mayindicate a partial area covered by the BS 11, and may refer to variouscoverage areas, such as a mega cell, a macro cell, a micro cell, a picocell, and a femto cell.

In this specification, a subject that may transmit and/or receive areference signal to/from the MS may be described with respect to aneNodeB, but aspects of the invention are not limited thereto.Accordingly, the subjects may be interpreted as including some or allsubjects that may be capable of transmitting and receiving signals,which may be differently expressed according to differences betweencommunication schemes and the like, or which may perform similar orequivalent operations.

In this specification, the MS (or UE) and the BS (or eNodeB), which maybe two transmission and/or reception subjects referred to with respectto exemplary embodiments or the technical aspects described in thisspecification are exemplary, and are not limited to a particularlydesignated term or word.

Hereinafter, downlink may indicate or signify communication or acommunication path from the BS 11 to the MS 12, and uplink may indicateor signify communication or a communication path from the MS 12 to theBS 11. In downlink, a transmitter may be a part of the BS 11, and areceiver may be a part of the MS 12. In uplink, a transmitter may be apart of the MS 12, and a receiver may be a part of the BS 11. However,aspects of the invention may not be limited thereto, such that variousaccess schemes may be applied to the wireless communication system 10.

For example, various multiple access schemes may include, withoutlimitation, a Code Division Multiple Access (CDMA), a Time DivisionMultiple Access (TDMA), a Frequency Division Multiple Access (FDMA), aOrthogonal Frequency Division Multiple Access (OFDMA), a SingleCarrier-FDMA (SC-FDMA), an OFDM-FDMA, an OFDM-TDMA, and an OFDM-CDMA.These modulation techniques may be used to demodulate signals receivedfrom multiple users of a communication system, and increase the capacityof the communication system. In this respect, use may be made of a TimeDivision Duplex (TDD) scheme in which uplink (UL) transmission anddownlink (DL) transmission may be performed at different times.Otherwise, use may be made of a Frequency Division Duplex (FDD) schemein which uplink transmission and downlink transmission may be performedby using different frequencies.

The wireless communication system 10 may be a CoMP system. The CoMPsystem may refer to a communication system that supports CoMP, or acommunication system to which the CoMP may be applied. The CoMP may be atechnology to coordinate or combine signals transmitted or received bymultiple transmission/reception points. The CoMP may increase a datatransmission rate or throughput, and may provide high quality of data.

A transmission/reception point may refer to, without limitation, atleast one of a component carrier, a cell, a base station (e.g., a macrocell, a pico eNodeB, or a femto eNodeB), and an RRH. Otherwise, thetransmission/reception point may refer to a set of antenna ports. Also,the transmission/reception point may transmit information from a set ofantenna ports to the MS through Radio Resource Control (RRC) signaling.Accordingly, multiple Transmission Points (TPs) in one cell may bereferred to as a set of antenna ports. An intersection between theantenna port sets may be an empty set.

BSs or cells may form multiple transmission/reception points,respectively. For example, the multiple transmission/reception pointsmay be macro cells forming a homogeneous network. Further, the multipletransmission/reception points may be a macro cell and RRHs having hightransmission power or a macro cell and RRHs having low transmissionpower in the macro cell area.

The CoMP system may selectively apply CoMP. A mode in which the CoMPsystem may perform communication by using the CoMP may be referred to asa CoMP mode. In contrast, a mode in which the CoMP system may notperform communication by using the CoMP may be referred to as a normalmode or a non-CoMP mode.

The MS 12 may be a CoMP terminal. The CoMP terminals may be elementsforming the CoMP system, and communicate with a CoMP set. One or moreCoMP terminals may also operate in a CoMP mode or in a normal mode,similarly to the CoMP system. Further, the CoMP set may be a set oftransmission/reception points, which directly and/or indirectlyparticipates in the transmission of data to the CoMP terminals on acertain time-frequency resource.

Direct participation in the transmission or reception of data mayindicate that transmission/reception points may transmit or receive datato or from the CoMP terminals on the relevant time-frequency resource.Indirect participation in the transmission or reception of data mayindicate that the transmission/reception points may not transmit orreceive data to or from the CoMP terminals on the relevanttime-frequency resource but may contribute to a determination of userscheduling/beamforming.

The CoMP terminals may simultaneously receive signals from the CoMP set,or may simultaneously transmit signals to the CoMP set. Further, theCoMP system may reduce an interference effect between CoMP sets in viewof a channel environment of one or more cells forming the CoMP set.

When operating the CoMP system, various scenarios may be available. Afirst CoMP scenario may correspond to a CoMP formed by a homogeneousnetwork of multiple cells in one BS, and may be called an intra-site. Asecond CoMP scenario may correspond to a CoMP formed by a homogeneousnetwork of one macro cell and one or more high-power RRHs. One or moreof a third CoMP scenario and a fourth CoMP scenario may correspond to aCoMP formed by a heterogeneous network of one macro cell and one or morelow-power RRHs in the macro cell area. When cell IDs of the RRHs are notidentical or do not correspond to a cell ID of the macro cell, suchscenario may correspond to the third CoMP scenario. Further, when thecell IDs of the RRHs are all identical or correspond to the cell ID ofthe macro cell, such scenario may correspond to the fourth CoMPscenario. However, aspects of the invention are not limited thereto,such that additional CoMP scenarios may be available.

The category of CoMP may include Joint Processing (JP) and CoordinatedScheduling/Beamforming (CS/CB), and it may be possible to mix JP withCS/CB.

With respect to JP, data on an MS may be used by at least onetransmission/reception point in a CoMP set on a certain time-frequencyresource. The JP may include, without limitation, Joint Transmission(JT) and Dynamic Point Selection (DPS).

JT may indicate multiple transmission/reception points belonging to aCoMP set may simultaneously transmit data to one MS or multiple MSs on atime-frequency resource. With respect to JT, multiple cells (i.e.,multiple transmission/reception points), which may transmit data to oneMS, may perform the transmission on an identical or correspondingtime/frequency resource.

With respect to DPS, one transmission/reception point in a CoMP set maytransmit data on a time-frequency resource. A transmission/receptionpoint may change in one or more subframes in view of interference. Thetransmitted data may be simultaneously used by multipletransmission/reception points. The DPS may include, without limitation,a dynamic cell selection.

With respect to the CS, one transmission/reception point in a CoMP setmay transmits data on a time-frequency resource, and user scheduling maybe determined by coordination among points in the relevant CoMP set.

With respect to the CB, user scheduling may also be determined bycoordination among points in the relevant CoMP set. Interferenceoccurring between an adjacent cell and MSs may be avoided by the CB.

The CS/CB may include Semi-Static Point Selection (SSPS) capable ofsemi-statically selecting a transmission/reception point and changingthe semi-statically selected transmission/reception point.

As described above, it may be possible to mix the JP with the CS/CB. Forexample, some transmission/reception points in a CoMP set transmit datato target MSs according to the JP, and the other transmission/receptionpoints in the CoMP set may perform the CS/CB.

A transmission/reception point may include, without limitation, a BS, acell, or an RRH. More specifically, a BS or an RRH may become atransmission/reception point. Further, multiple BSs and/or RRHs maybecome multiple transmission/reception points. Although thespecification may be described with respect to BHs and RRHs, aspects ofthe invention are not limited thereto, such that operations of all BSsor RRHs may be applied to other types of transmission/reception points.

Further, control information of a physical layer mapped to a PhysicalDownlink Control Channel (PDCCH) may be used in the physical layer maybe referred to as Downlink Control Information (DCI). The DCI may betransmitted through the PDCCH. Further, the DCI may include an uplink ordownlink resource allocation field, uplink transmission power controlinstruction field, a control field for paging, a control field forinstructing a Random Access (RA) response, and the like.

According to the format of the DCI, the use of the DCI changes, and thetype of a field defined in the DCI may also change. Table 1 may show theDCI according to the DCI format.

TABLE 1 DCI format Description 0 used for the scheduling of PUSCH(uplink grant) 1 used for the scheduling of one PDSCH codeword in onecell 1A used for the compact scheduling of one PDSCH codeword in onecell and a random access procedure initiated by a PDCCH instruction 1Bused for the compact scheduling of one PDSCH codeword in one cell, whichuses precoding information 1C used for the compact scheduling of onePDSCH codeword and the notification of change of NCCH 1D used for thecompact scheduling of one PDSCH codeword in one cell, which includesprecoding and power offset information 2 used for the PDSCH schedulingof MSs configured in a spatial multiplexing mode 2A used for the PDSCHscheduling of MSs configured in a large-delay CDD mode 2B used in atransmission mode 8 (dual-layer transmission) 2C used in a transmissionmode 9 (multi-layer transmission) 3 used for the transmission of TPCinstructions for PUCCH and PUSCH, which includes 2-bit power adjustments3A used for the transmission of TPC instructions for PUCCH and PUSCH,which includes single bit power adjustments 4 used for the scheduling ofPUSCH (uplink grant), and particularly, used for the PUSCH scheduling ofMSs configured in a spatial multiplexing mode

Referring to Table 1, the DCI includes the DCI format 0 indicatinguplink scheduling information, the format 1 for the scheduling of onePDSCH codeword, the format 1A for the compact scheduling of one PDSCHcodeword, the format 10 for a more compact scheduling of Downlink SharedChannel (DL-SCH), the format 2 for PDSCH scheduling in a closed-loopspatial multiplexing mode, the format 2A for PDSCH scheduling in anopen-loop spatial multiplexing mode, the format 3 and format 3A each forthe transmission of a Transmission Power Control (TPC) instruction foran uplink channel and the like.

Fields of the DCI may be sequentially mapped to an n number ofinformation bits a₀ to a_(n-1), respectively. For example, when the DCIis mapped to information bits having a total length of 44 bits, fieldsof the DCI may be sequentially mapped to a range of a₀ to a₄₃,respectively. The DCI format 0, format 1A, format 3 and format 3A mayhave a similar or an identical payload size. The DCI format 0 may alsobe called an uplink grant.

In the wireless communication system, it may be possible to estimate anuplink channel or a downlink channel for the purpose of the transmissionand reception of data, the acquisition of system synchronization, thefeedback of channel information, and the like. A process forreconstructing a transmission signal by compensating for the distortionof a signal, which may result from a sudden change in a channelenvironment, may be referred to as channel estimation. Also, a channelstate of a cell (or point), to which an MS belongs or another cell (orpoint) may be measured. Further, a reference signal known to both the MSand a transmission/reception point may be used to estimate a channel ormeasure a channel state.

Because the MS may know or be aware of information of the referencesignal, it may estimate a channel and may compensate for a channel valuebased on the received reference signal. Further, the MS may accuratelyobtain data transmitted by the transmission/reception point.

Further, a reference signal may be generated and transmitted based on asequence of the reference signal. One or more of various sequenceshaving excellent or reference correlation characteristics may be used assequences for the reference signal. For example, a Constant AmplitudeZero Auto-Correlation (CAZAC) sequence of a Zadoff-Chu (ZC) sequence andthe like, or a pseudo-noise (PN) sequence of an m-sequence, a Goldsequence, a Kasami sequence and the like may be used as a sequence forthe reference signal. In addition, according to system conditions,various other sequences having excellent or reference correlationcharacteristics may be used as sequences for the reference signal. Also,in order to adjust the length of the reference signal sequence, thereference signal sequence may first be subjected to cyclic extension ortruncation, and may then be used. Further, the reference signal sequencemay first be modulated in various forms, for example, by using BinaryPhase Shift Keying (BPSK) or Quadrature Phase Shift Keying (QPSK), andmay then be mapped to a Resource Element (RE).

Downlink reference signals may include a Cell-specific Reference Signal(CRS), a Multimedia Broadcast and multicast Single Frequency NetworkReference Signal (MBSFNRS), a UE-specific Reference Signal or aDemodulation Reference Signal (DM-RS) according to the use of thesignal, a Positioning Reference Signal (PRS), and a Channel StateInformation Reference Signal (CSI-RS).

The CRS, which may be a reference signal transmitted to some or all MSsin a cell, may be used to estimate a channel. The CRS may be transmittedthrough some or all downlink subframes in a cell, which may supportPDSCH transmission.

The UE-specific RS or the DM-RS, which may be a reference signalreceived by a particular MS or a particular MS group in a cell, may beused for the demodulation of data in the particular MS or the particularMS group.

The MBSFN RS may be a reference signal to provide a Multimedia BroadcastMulticast Service (MBMS), and the PRS may be used as a reference signalto measure the location of an MS.

The CSI-RS may be used to estimate channel state information. The CSI-RSmay be arranged in the frequency or time domain. The MS may report atleast one of a Channel Quality Indicator (CQI), a Precoding MatrixIndicator (PMI) and a Rank Indicator (RI) as channel state informationthrough the estimation of a channel state which uses the CSI-RS. TheCSI-RS may be transmitted from one or more antenna ports.

In the CoMP system, multiple cells or transmission/reception points mayalso transmit reference signals to MSs.

In a CoMP environment, consideration may be given to a method and anapparatus to ensure the orthogonality of an existing reference signal,which may be configured in the conventional single cell, even inmultiple cells or TPs. More specifically, consideration may be given toboth a method and an apparatus to generate a reference signal sequence,which may be integrated by considering the existing MIMO environment andthe above CoMP environment, and a method and an apparatus to signalinformation related to the generation of the reference signal sequence.

FIG. 2 is a diagram illustrating a macro cell and RRHs forming a CoMPset and UEs performing transmission and reception with the cells andRRHs according to an exemplary embodiment of the present invention.

As shown in FIG. 2, a first UE 0, a second UE 1, a third UE 2 and afourth UE 3 may be connected to a first TP 0, a second TP 1, a third TP2 and a fourth TP 3, respectively. The first UE 0, the second UE 1, thethird UE 2 and the fourth UE 3 have the first TP 0, the second TP 1, thethird TP 2 and the fourth TP 3 as their serving cells or points,respectively. Referring to FIG. 2, where the first TP 0 is matched to amacro cell, the second TP 1 is matched to a first RRH 1, the third TP 2is matched to a second RRH 2, and the TP 3 may be matched to a third RRH3. Also, at least one of the first UE 0, the second UE 1, the third UE 2and the fourth UE 3 may share a bandwidth allocated to each UE and apart or the whole of a bandwidth allocated to the other UEs atfrequencies between them.

Further, when a reference signal, such as a DM-RS, is transmitted fromeach cell to a UE in the wireless communication system, such as longterm evolution (LTE), a sequence for a reference signal may be generatedas shown in Equation (1) below. The generated reference signal sequencemay be mapped to a Resource Element (RE), and a signal may be generatedand the generated signal may be transmitted to one or more UEs.

$\begin{matrix}{\mspace{79mu}{{{r(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{{{where}\mspace{14mu} m} = \left\{ {\begin{matrix}{0,1,\ldots\mspace{11mu},{{12N_{RB}^{\max.{DL}}} - {1\mspace{14mu}{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}} \\{0,1,\ldots\mspace{11mu},{{16N_{RB}^{\max.{DL}}} - {1\mspace{14mu}{extended}\mspace{11mu}{cyclic}\mspace{14mu}{prefix}}}}\end{matrix},{{{and}\mspace{79mu} c_{init}} = {{\left( {\left\lfloor {n_{g}/2} \right\rfloor + 1} \right) \cdot \left( {{2N_{ID}^{cell}} + 1} \right) \cdot 2^{16}} + n_{SCID}}}} \right.}}} & (1)\end{matrix}$

In Equation (1), a reference signal sequence r(m) is generated from a PNsequence (c(2m) and c(2m+1)) along the real axis and the imaginary axison the complex plane. c_(init) may refer to an initialization value ofthe PN sequence that may have a value, which changes according to a slotnumber n_(s), a cell ID N_(ID) ^(cell), and the value of a ScramblingCode Identity (SCID) n_(SCID).

In Equation (1), a DCI format 2B capable of using antenna port 7 and/orport 8, the SCID n_(SCID) may be indicated by 1-bit information on ascrambling identity. Also, referring to a DCI format 2C capable of usingat least one of an antenna port 7, an antenna port 8, an antenna port 9,an antenna port 10, an antenna port 11, an antenna port 12, an antennaport 13, and an antenna port 14, the SCID n_(SCID) may be indicated by3-bit information on antenna port(s), a scrambling identity and thenumber of layers, which are included in the DCI format 2C, as shown inTable 2 below. More specifically, as shown in Table 2, in the DCI format2C, the SCID has a value of 0 or 1 for the antenna port 7 and/or theantenna port 8, and may have a value of 0 for the other antenna ports.

TABLE 2 One Codeword: Two Codewords: Codeword 0 enabled and Codeword 0enabled and Codeword 1 disabled Codeword 1 enabled Value Message ValueMessage 0 1 layer, port 7 and n_(SCID) = 0 0 2 layers, ports 7-8 andn_(SCID) = 0 1 1 layer, port 7 and n_(SCID) = 1 1 2 layers, ports 7-8and n_(SCID) = 1 2 1 layer, port 8 and n_(SCID) = 0 2 3 layers and ports7-9 3 1 layer, port 8 and n_(SCID) = 1 3 4 layers and ports 7-10 4 2layers and ports 7-8 4 5 layers and ports 7-11 5 3 layers and ports 7-95 6 layers and ports 7-12 6 4 layers and ports 7-10 6 7 layers and ports7-13 7 Reserved 7 8 layers and ports 7-14 or One Codeword: TwoCodewords: Codeword 0 enabled and Codeword 0 enabled and Codeword 1disabled Codeword 1 enabled Value Message Value Message 0 1 layer, port7 and SCID = 0 0 2 layers, ports 7-8 and SCID = 0 1 1 layer, port 7 andSCID = 1 1 2 layers, ports 7-8 and SCID = 1 2 1 layer, port 8 and SCID =0 2 3 layers, ports 7-9 and SCID = 0 3 1 layer, port 8 and SCID = 1 3 4layers, ports 7-10 and SCID = 0 4 2 layers, ports 7-8 and SCID = 0 4 5layers, ports 7-11 and SCID = 0 5 3 layers, ports 7-9 and SCID = 0 5 6layers, ports 7-12 and SCID = 0 6 4 layers, ports 7-10 and SCID = 0 6 7layers, ports 7-13 and SCID = 0 7 Reserved 7 8 layers, ports 7-14 andSCID = 0

Further, a current method for generating a reference signal sequence, asshown in Equation (1) may be defined specifically for a single cell.Accordingly, in an environment, such as a CoMP environment, wheremultiple cells or points are considered, a problem may occur in theorthogonality of reference signals.

FIG. 3 is a diagram illustrating an environment facilitating atransmission of reference signals from Transmission Points (TPs) tomultiple mobile stations according to an exemplary embodiment of thepresent invention.

As shown in FIG. 3, the TP 0 corresponding to a macro cell transmits areference signal to one or more of the UE 0 and the UE 1 on an identicaltime-frequency resource. Accordingly, this situation may be regarded asan example of MU-MIMO. In order to distinguish between {circle around(m)}-{circle around (o)} and {circle around (m)}-{circle around (1)}corresponding to two reference signals simultaneously transmitted to theUE 0 and the UE 1 on a time-frequency resource, the two referencesignals {circle around (m)}-{circle around (o)} and {circle around(m)}-{circle around (1)} may use an identical reference signal sequence,and may be distinguished from each other by using an orthogonalsequence, such as an Orthogonal Cover Code (OCC). However, aspects ofthe invention are not limited thereto, such that TP 0 may transmit areference signal to one or more of the UE 0 and UE 1 on a similar orcorresponding time-frequency resource. Further, two reference signalsmay be transmitted to the UE 0 and the UE 1 within a reference timeperiod.

Also, the RRH 1 (i.e., TP 1) transmits a reference signal to the UE 1.When the UE 1 is a CoMP UE as shown in FIG. 3, the UE 1 simultaneouslyreceives reference signals {circle around (m)}-{circle around (1)} and{circle around (1)} from the TP 0 corresponding to the macro cell aswell as from the RRH 1 on a time-frequency resource according to JointTransmission (JT) CoMP. Further, the two reference signals {circlearound (m)}-{circle around (1)} and {circle around (1)} may also use anidentical or corresponding reference signal sequence. Therefore, thereference signals {circle around (m)}-{circle around (o)}, {circlearound (m)}-{circle around (1)}, and {circle around (1)} as illustratedin FIG. 3 may use an identical or corresponding reference signalsequence.

When MU-MIMO and CoMP are not simultaneously supported on an identicaltime-frequency resource, three reference signal sequences as illustratedin FIG. 3 may not be identical. More specifically, when the MU-MIMO issupported, {circle around (m)}-{circle around (o)} and {circle around(m)}-{circle around (1)} may use an identical or corresponding referencesignal sequence. When the CoMP is supported, {circle around (m)}-{circlearound (1)} and {circle around (1)} may use an identical orcorresponding reference signal sequence.

Further, as shown in FIG. 3, the RRH 2 (i.e., TP 2) and the RRH 3 (i.e.,TP 3) transmit reference signals to the UE 2 and the UE 3, respectively.More specifically, an example of a method in which the RRH 2 and the RRH3 transmit signals to the UE 2 and the UE 3 in the CoMP environment,respectively, may be DPS or CS/CB, but the exemplary embodiments of thepresent invention may not be limited thereto. The RRH2 may transmit thereference signal {circle around (2)} to the UE 2, and the referencesignal {circle around (2)} may act as interference {circle around(2)}-{circle around (i)} from the viewpoint of the UE 0. Similarly, theRRH 3 may transmits a reference signal {circle around (3)} to the UE 3,but the reference signal {circle around (3)} may act as interference{circle around (3)}-{circle around (i)} from the viewpoint of the UE 2.

More specifically, in order to solve the problem of interference (e.g.,interference between {circle around (m)}-{circle around (o)} and {circlearound (2)}-{circle around (i)} in the UE 0 and interference between{circle around (2)} and {circle around (3)}-{circle around (i)} in theUE 2 in FIG. 3), different reference signal sequences may be used.

Accordingly, in the CoMP environment where multiple cells or points areconsidered as well as a single cell, one or more TPs (e.g., TP 0 and TP1 that may simultaneously transmit signals to the UE 1 on atime-frequency resource) that may be configured to transmit signals to aparticular UE (e.g., UE 1), may transmit an identical, similar, orcorresponding reference signal. However, one or more TPs (e.g., TP 2 andTP 3 that transmit signals to the UE 2 and the UE 3, respectively) thatdo not transmit signals to the particular UE (e.g., the UE 1) maygenerate different reference signal sequences to generate and transmitreference signals different from the reference signal transmitted to theparticular UE.

More specifically, in the CoMP environment where the multiple cells orpoints may be considered as well as the single cell, when the cells orTPs transmit reference signals to the UEs, at least one of a referencesignal transmitted from the TP 2 (i.e., RRH 2) to the UE 2 and areference signal transmitted from the TP 3 (i.e., RRH 3) to the UE 3 mayrequest generation of different reference signal sequences. According toaspects of the invention, the cells or TPs transmit reference signals tothe UEs to give or provide pseudo orthogonality of the referencesignals.

Further, at least one of a reference signal {circle around (m)}-{circlearound (o)} transmitted from the TP 0 (i.e., macro cell) to the UE 0 andreference signals {circle around (m)}-{circle around (1)} and {circlearound (1)} transmitted from the TP 0 (i.e., macro cell) and the TP 1(i.e., RRH 1) to the UE 1 may have an identical, similar, orcorresponding reference signal sequence. However, in order to give thepseudo orthogonality of reference signals, at least one of the referencesignals {circle around (m)}-{circle around (o)}, {circle around(m)}-{circle around (1)} and {circle around (1)} a reference signal{circle around (2)} transmitted from the TP 2 (RRH 2) to the UE 2, and areference signal transmitted from the TP 3 (RRH 3) to the UE 3, may havedifferent reference signal sequences.

As described above, one or more CoMP scenario may use a method forgenerating a reference signal sequence to transmit identical ordifferent reference signal sequences to multiple UEs. The method withrespect to below scenario types will be described in more detail below.

Scenario type 1: When cells or TPs have different cell IDs (, CoMPscenarios 1, 2, and 3).

Scenario sub-type 1: An algorithm for generating identical referencesignal sequences.

A sequence may be generated based on a common cell ID, which may becommon between the cells, differently from Equation (1), to generateidentical, similar, or corresponding reference signal sequences despitedifferent cell IDs of TPs in view of the inter-cell orthogonality ofreference signals. For example, at least one of the reference signal{circle around (m)}-{circle around (o)} transmitted from the TP 0 (i.e.,macro cell) to the UE 0, and the reference signals {circle around(m)}-{circle around (1)} and {circle around (1)} transmitted from the TP0 (i.e., macro cell) and the TP 1 (i.e., RRH 1) to the UE 1, asillustrated in FIG. 3, may request to generate a reference signalsequence based on an identical cell ID.

When the CoMP and the MU-MIMO are not simultaneously supported on anidentical time-frequency resource, there may be nothing to change fromthe viewpoint of a UE. More specifically, one or more UEs may follow acell ID of a cell or a transmission/reception point, to which therespective UE may belong. Accordingly, one or more UEs may not beseparately notified of information on the common cell ID, which may becommon between the cells. An eNodeB may know of the information on thecommon cell ID, and may generate a sequence based on the common cell ID.More specifically, from the viewpoint of the eNodeB, a method forgenerating a reference signal sequence may change.

When the CoMP and the MU-MIMO are simultaneously supported on anidentical time-frequency resource, a cell ID of a cell or atransmission/reception point to which one or more UE may belong, maydiffer from the common cell ID. Accordingly, one or more UEs may beseparately notified of the information on the common cell ID, which maybe common between the cells. The eNodeB may generate a sequence based onthe common cell ID. More specifically, from the viewpoint of the eNodeBand the UE, conditions related to the reference signal sequences may bechanged from the existing ones.

Scenario sub-type 2: An algorithm for generating different referencesignal sequences

In this scenario sub-type, the TPs may have different cell IDs.Accordingly, the method for generating a cell-specific reference signalsequence as shown in Equation (1) may sufficiently enable the generationof different reference signal sequences. More specifically, from theviewpoint of the eNodeB and the UE, conditions related to the referencesignal sequences may not be changed from the existing ones.

Further, it may be possible to generate different reference signalsequences according to the UEs or TPs to further subdivide the referencesignal sequences.

Scenario type 2: When cells or TPs all have an identical cell ID (e.g.,CoMP scenario 4)

Scenario sub-type 1: An algorithm for generating identical referencesignal sequences

When the TPs have different cell IDs, a sequence may be generated basedon a common cell ID, which may be common between the cells, differentlyfrom Equation (1), in order to generate identical reference signalsequences. However, the CoMP scenario 4 may have a CoMP environmentwhere some or all points may have an identical cell ID. Thus, the CoMPscenario 4 may correspond to an environment where some or all points mayalready use a common cell ID as their cell IDs. Accordingly, the methodfor generating a cell-specific reference signal sequence as shown inEquation (1) may sufficiently enable the generation of differentreference signal sequences. More specifically, from the viewpoint of theeNodeB and the UE, conditions related to the reference signal sequencesmay not have to be changed from the existing ones.

Scenario sub-type 2: An algorithm for generating different referencesignal sequences

In this scenario sub-type, the TPs may have an identical cell ID.Accordingly, the method for generating a cell-specific reference signalsequence as shown in Equation (1) may not enable the generation ofdifferent reference signal sequences. Accordingly, it may be possible tomodify the method for generating a reference signal sequence as shown inEquation (1) and generate reference signal sequences different accordingto the UEs or TPs. Further, the initialization value c_(init) as definedby Equation (1) may be set differently for one or more UEs or TPs togenerate different reference signal sequences. Information used to setthe initialization value different for one or more UEs or TPs may bedefined as initialization value generation information.

More specifically, the initialization value generation information forgenerating reference signal sequences, which may be different accordingto the UEs or TPs, may be transmitted from the TP to UEs. Accordingly,from the viewpoint of the TP (or eNodeB) and the UE, conditions relatedto the reference signal sequences may be changed from the existing ones.

When the reference signal sequences are generated according to the aboveschemes and information associated with the generation of the referencesignal sequences is signaled to the UE as described above, a referencesignal may be generated and the generation of the reference signal maybe signaled to the UE. The reference signal sequence generation andsignaling of information associated with the generation of the referencesignal sequence may be performed to separately consider one or more CoMPscenario environment and the existing single cell environment. However,it may be more effective to use a generation method and a signalingmethod, which may be integrated as one element.

Further, according to exemplary embodiments of the present inventionprovide a method for using multiple initialization values, such as afirst initialization value for generating identical sequences(hereinafter, referred to as a “first initialization value” or an“initialization value A”) and a second initialization value forgenerating a different sequence (hereinafter, referred to as “secondinitialization values” or “initialization values B”), as theinitialization value for the sequence used during the generation of adownlink reference signal sequence. Further, one of the twoinitialization values may be selected and a sequence may be generatedaccording to conditions of one or more UEs, in which instructioninformation related to such a selection may be signaled to one or moreUEs.

Hereinafter, various methods of value generation may be provided,including (1) a method for generating an initialization value A (e.g.,first initialization value) and (2) a method for generating aninitialization value B (e.g., second initialization value). Theinitialization value generation information that may be used to generatethe initialization value A and the initialization values B may bedescribed in more detail below.

(1) The method for generating an initialization value for generatingidentical sequences (i.e., initialization value A or firstinitialization value) may be described in more detail below.

If a cell-specific initialization value used in Equation (1) is used,information, which may normally be separately and additionally signaledto the UE, may not exist. More specifically, a general communicationenvironment, which may not be a case where multiple TPs have differentcell IDs as in the CoMP scenarios 1, 2, or 3, may not request or useseparate initialization value generation information, which may provideone or more reference signal sequences to be identical. Thus, thegeneral communication environment may not signal the initializationvalue generation information to one or more UEs.

When the MU-MIMO and the CoMP are simultaneously considered wheremultiple TPs have different cell IDs, a common cell ID, which may berepresentative of the whole of a CoMP set, may be used instead of thecell ID N_(ID) ^(cell) for calculating the initialization value c_(init)as defined by Equation (1).

Further, the common cell ID may be previously transmitted to the UEthrough high layer signaling, such as RRC. Although this common cell IDinformation may have 9 bits, aspects of the invention may not be limitedto such a configuration. However, even when the common cell ID may beused, in the CoMP scenario 4 or in a non-CoMP environment, the commoncell ID may be identical, similar, or corresponding to a cell ID of acell or a TP, to which a UE may belong. Accordingly, although thesignaling may not be separately performed or may be separatelyperformed, the common cell ID may become the cell ID of the cell or TP,to which the UE may belong.

More specifically, as the initialization value A, a cell-specificinitialization value used in Equation (1) may be used or a CoMPset-specific initialization value may be used. When a cell-specificinitialization value is used, signaling information, which may beseparately indicated, may not exist. When a CoMP set-specificinitialization value is used, the common cell ID information may besignaled or transmitted, as initialization value generation information,to one or more UEs. To perform the signaling or transmitting operationof the common cell ID information, high layer signaling, such as RRC maybe used.

(2) The method for generating an initialization value for generating adifferent sequence (e.g., initialization value B or secondinitialization value) may be described in more detail below.

When multiple TPs have an identical cell ID, an initialization value ofa cell-specific reference signal sequence as defined by Equation (1) maynot enable the generation of different reference signal sequences.Accordingly, the method for generating a reference signal sequence asshown in Equation (1) may be modified and different initializationvalues of reference signal sequences according to the UEs or TPs may begenerated. Initialization value generation information capable ofgenerating the changed initialization values may be indicated to theUEs.

Further, when multiple TPs have different cell IDs, an initializationvalue of a cell-specific reference signal sequence as defined byEquation (1) may be sufficient as initialization values for generatingdifferent sequences. However, although the method for generating areference signal sequence as shown in Equation (1) may be modified andthe different initialization values of the reference signal sequencesaccording to the UEs or TPs may be generated, the different sequencesmay be generated. Accordingly, the modified method may be appliedequally.

The method for generating different initialization values of referencesignal sequences according to the UEs or TPs may include, withoutlimitation, one of the following methods. Initialization valuegeneration information for generating the initialization values may bedefined or transmitted in advance or ad hoc to the UEs through highlayer signaling, such as RRC, so that the UEs may be aware of theinitialization value generation information. As described below, in thismethod, n_(SCID) of Equation (1), which may be an initialization valuegeneration information for generating different initialization valuesmay be replaced by n_(RNTI) or n′_(SCID). Different initializationvalues maybe denoted by c_(init).

A first method, in which a Radio Network Temporary Identifier (RNTI) maybe used.

An RNTI value may be used in place of n_(SCID) as shown in Equation (1)(e.g., the parameter n_(SCID) as shown in Equation (1) may be changed toa parameter n_(RNTI)). Accordingly, an initialization value of asequence for a reference signal may be set differently for one or moreUEs. Based on the initialization value, a reference signal sequence maybe generated, which may be mapped to an RE, and a signal may begenerated to be transmitted to one or more UEs.

Further, because one or more UEs may already know the RNTI,initialization value generation information, which may be signaled, mayhave a value of 0 bits.

More specifically, in the first method, RNTI of each UE may be used(i.e., n_(RNTI) may replace n_(SCID) in Equation (1)) as initializationvalue generation information to generate a different reference signalsequence for one or more UEs. However, because one or more UEs mayalready know the RNTI thereof, the initialization value generationinformation may not be separately signaled to one or more UEs.

A second method, in which separate UE-specific information may be used.

In the second method, separately-defined UE-specific information may beused as initialization value generation information, and thisUE-specific information may be denoted by n′_(SCID).

More specifically, in the second method, a parameter that may betransmitted through high layer signaling, such as UE-specific RRC, maybe used in place of n_(SCID) as shown in Equation (1). For example, theparameter n_(SCID) may be changed to a parameter n′_(SCID). Further,N-bit, in which N may be a natural number equal to or greater than 1,information may be used as UE-specific information, which may be set asn′_(SCID). By using the N-bit information, different reference signalsequences according to a maximum number 2^(N) of UEs, which maysimultaneously transmit reference signals on a time-frequency resource,may be generated and allocated to the UEs. Accordingly, it may bepossible to give or provide the pseudo orthogonality of the referencesignals.

Accordingly, in the second method, the separate UE-specific informationof N bits may be used as initialization value generation information,and this UE-specific information may be transmitted to one or more UEsthrough RRC signaling or the like.

A third method, in which separate TP-specific information may be used.

In the third method, separately-defined TP-specific information may beused as initialization value generation information, and thisTP-specific information may be denoted by n′_(SCID).

More specifically, in the third method, a parameter may be transmittedthrough high layer signaling, such as RRC, which may be specific for aTP. Further, the parameter may be used in place of n_(SCID) as shown inEquation (1). For example, the parameter n_(SCID) may be changed to aparameter n′_(SCID). Here, N-bit, in which N is a natural number equalto or greater than 1, information may be used as TP-specificinformation, which may be set as n′_(SCID). By using the N-bitinformation, different reference signal sequences according to a maximumnumber 2^(N) of TPs, which may simultaneously transmit reference signalson a time-frequency resource, may be generated and allocated to the UEs.Accordingly, it may be possible to give the pseudo orthogonality of thereference signals.

Thus, in the third method, the separate TP-specific information of Nbits may be used as initialization value generation information, andthis TP-specific information may be transmitted to one or more UEsthrough RRC signaling or the like.

A fourth method, in which a CSI-RS antenna port and/or CSI-RSconfiguration information may be used.

In the fourth method, a parameter determined in relation to a CSI-RSantenna port and/or CSI-RS configuration information may be used inplace of n_(SCID) as shown in Equation (1). More specifically, aparameter n′_(SCID) determined in relation to the CSI-RS antenna portand/or the CSI-RS configuration information may be used asinitialization value generation information. The use of the parametern′_(SCID) as the initialization value generation information may beexpressed by changing the parameter n_(SCID) as shown in Equation (1) ton′_(SCID).

According to exemplary embodiments, CSI-RS antenna port informationhaving a value of 15 to 22, or CSI-RS configuration information having avalue of 0 to 31, or a parameter drawn from the CSI-RS antenna portinformation and/or the CSI-RS configuration information may be used asinitialization value generation information n′_(SCID). Further, anexample of the initialization value generation information n′_(SCID) maybe as follows.n′ _(SCID)=(CSI-RS antenna port number)−7(or n′ _(SCID)=(CSI-RS antenna port number)−8),or;n′ _(SCID)=(CSI-RS configuration number)(or n′ _(SCID)=(CSI-RS configuration number)+1)

A sequence for a reference signal may be generated based on theinitialization value generation information n′_(SCID), which may bemapped to an RE, and a signal may be generated to be transmitted to oneor more UEs. Further, because one or more UEs may be aware of the CSI-RSantenna port and/or the CSI-RS configuration information through anothersignaling for a CSI-RS, signaled bits may be 0 bits.

More specifically, in the fourth method, in order to generate areference signal sequence different for one or more UEs or TPs, theCSI-RS antenna port information, or the CSI-RS configuration informationhaving a value of 0 to 31, or the parameter drawn from the CSI-RSantenna port information and/or the CSI-RS configuration information maybe used (e.g., n′_(SCID) replaces n_(SCID) in Equation (1)) as theinitialization value generation information. However, because one ormore UEs may already be aware of this information through anothersignaling, the initialization value generation information may not beseparately signaled to one or more UEs.

As described above, a method according to an exemplary embodiment of thepresent invention may include: selectively generating one of a referencesignal identical, similar, or corresponding for one or more UEs or TPsand a reference signal different for one or more UEs or TPs, andtransmitting the generated reference signal to one or more UEs, by a TP;and generating selection instruction information on whether thetransmitted reference signal is a reference signal similar or differentfor one or more UEs or TPs, and transmitting the generated selectioninstruction information to one or more UEs, by the TP. The describedmethod may be suitable for one or more of the UEs according to acommunication environment, such as the CoMP, the MU-MIMO, and the like,

Also, the method according to an exemplary embodiment of the presentinvention may further include generating initialization value generationinformation capable of changing an initialization value of a sequencefor the reference signal, which may be generated to be transmitted, andtransmitting the generated initialization value generation informationto the relevant UE. Further, the initialization value generationinformation may include at least one of a common cell ID, RNTI,UE-specific information, TP-specific information, and a parameterrelated to a CSI-RS, and may be transmitted through high layersignaling, such as RRC.

Further, the initialization value generation information may not beseparately signaled to each UE according to the type of a communicationsystem.

Also, the selection instruction information on whether the transmittedreference signal is a reference signal similar or different for one ormore UEs or TPs may be implicitly indicated by information included in aDCI format, or may be explicitly indicated by separate bits included inDCI.

When the selection instruction information is implicitly indicated, theselection instruction information may be indicated by 1-bit ScramblingCode Identity (n_(SCID) or SCID) information that may be included in aDCI format 2B, or by information on antenna port(s), a scramblingidentity, and the number of layers, which may be included in a DCIformat 2C.

Also, when the selection instruction information is explicitlyindicated, the selection instruction information may be indicated by a1-bit additional instruction bit separately added to a DCI format, ormay be indicated by at least one of a table of information on antennaport(s), a scrambling identity, and the number of layers, which may benewly formed or defined by 4 bits of the DCI format.

As described above, in an exemplary embodiment of the present invention,a dynamic determination may be made as to which initialization value isto be selected from among the initialization value A and initializationvalue B according to conditions of one or more UEs, and information(e.g., selection instruction information) related to this determinationmay be transmitted to one or more UEs. Further, a method for configuringthis selection instruction information may include at least one of thefollowing four methods described below. However, aspects of theinvention are not limited to thereto.

A method 1 for generating selection instruction information is describedin more detail below. The method 1 may be a method in which the existinginstruction information related to a DM-RS of Table 2 is used as it is.

The method 1 for generating selection instruction information may usethe reference signal instruction information previously defined as inTable 2, and may use the reference signal instruction information forimplicit indication.

More specifically, a SCID value, which may be a first value included ininformation on antenna port(s), and a scrambling identity and a numberof layers information, which may be 3-bit information of the DCI format2C as shown Table 2, may be used for indication. When SCID=0, aninitialization value A (i.e., an initialization value for generatingidentical reference signal sequences) may be generated. When SCID=1,initialization values B (i.e., initialization values for generatingdifferent reference signal sequences) may be generated. Further, whenSCID=1, the initialization value A (i.e., the initialization value forgenerating identical reference signal sequences) may be generated. WhenSCID=0, the initialization values B (i.e., the initialization values forgenerating different reference signal sequences) may be generated.

When Equation (1) is modified in order to express this configuration ofthe method 1, Equation (2) below may be obtained. Equation (2) mayprovide information for transmitting the existing SCID, such as valuesof Table 2.

$\begin{matrix}{\mspace{79mu}{{{r(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{{{where}\mspace{14mu} m} = \left\{ {\begin{matrix}{0,1,\ldots\mspace{11mu},{{12N_{RB}^{\max.{DL}}} - {1\mspace{14mu}{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}} \\{0,1,\ldots\mspace{11mu},{{16N_{RB}^{\max.{DL}}} - {1\mspace{14mu}{extended}\mspace{11mu}{cyclic}\mspace{14mu}{prefix}}}}\end{matrix},{{{and}\mspace{79mu} c_{init}} = {{{\left( {\left\lfloor {n_{g}/2} \right\rfloor + 1} \right) \cdot \left( {{2N_{ID}^{cell}} + 1} \right) \cdot 2^{16}} + {n_{A}\mspace{20mu}{where}\mspace{14mu} n_{A}}} = \left\{ {{\begin{matrix}0 & {{{if}\mspace{14mu}{SCID}} = 0} \\{n_{RNTI}\mspace{14mu}{or}\mspace{14mu} n_{SCID}^{\prime}} & {{{if}\mspace{14mu}{SCID}} = 1}\end{matrix}\mspace{14mu}{or}\mspace{20mu} n_{A}} = \left\{ \begin{matrix}{n_{RNTI}\mspace{14mu}{or}\mspace{14mu} n_{SCID}^{\prime}} & {{{if}\mspace{14mu}{SCID}} = 0} \\{0\mspace{14mu}{or}\mspace{14mu} 1} & {{{if}\mspace{14mu}{SCID}} = 1}\end{matrix} \right.} \right.}}} \right.}}} & (2)\end{matrix}$

Further, in Equation (2), values for determining a sequenceinitialization value c_(init) include a cell ID N_(ID) ^(cell), n_(A),and the like. As compared with Equation (1), in Equation (2), as includedescribed above, the cell ID N_(ID) ^(cell) may become a common cell IDor may be a cell ID of a cell or a TP, to which a UE belongs, as inEquation (1). Also, n_(SCID) as shown in Equation (1) may be replaced byn_(A) representing initialization value generation information accordingto an exemplary embodiment of the present invention, and may bedifferently set according to generation of the initialization value A orthe initialization values B according to the existing signaled SCIDvalue.

Further, although n_(A) may signify a parameter, which may replacen_(SCID) when n_(A) has the same or similar meaning as the n_(SCID),exemplary embodiments of the present invention may not limited tonotation of the scheme as described above. Accordingly, n_(A) may bedenoted in other schemes than the scheme described above. For example,n_(SCID) may be used as an identical or corresponding parameter.

Initialization value generation information may be used to change to theinitialization value A identical, similar, or corresponding to one ormore UEs or TPs or different initialization value B for one or more UEsor TPs. Further, the initialization value generation information may beused to change to the initialization value A or initialization value Bin response to the selection instruction information, which may includeat least one of a cell ID N_(ID) ^(cell), a common cell ID, RNTIinformation, separately-defined UE-specific information,separately-defined TP-specific information, and a parameter related to aCSI-RS. When information that one or more UEs may not know exists amongthem, an eNodeB may transmit the relevant initialization valuegeneration information to the respective UE or UEs through RRC signalingor the like. Further, among the initialization value generationinformation, the RNTI information may be represented by n_(RNTI), and avalue different from n_(SCID), such as the separately-definedUE-specific information, the separately-defined TP-specific information,the parameter related to the CSI-RS or the like, may be represented byn′_(SCID).

A method 2 for generating selection instruction information is describedin more detail below. The method 2 may be a method in which the existinginstruction information related to a DM-RS of Table 2 is used as it is.

The method 2 for generating selection instruction information may usethe reference signal instruction information previously defined as inTable 2, and may use separate explicit instruction bits.

In the method 2, separate 1-bit selection instruction information may beincluded in a DCI format. More specifically, information added to DCImay not exist in the method 1, whereas 1 bit may be included in the DCIin the method 2. In the case of the method 2, the equation forcalculating an initialization value as defined by Equation (1) may bereplaced by Equation (3) and Equation (4) below. In each of Equation (3)and Equation (4) below, a formula expressing a reference signal sequencer(m) may be similar or the same as that in Equation (1), and may not bedescribed in more detail.

For reference, Equation (3) may correspond to a situation where the1-bit information, which may have a value of 0 or 1, additionallyincluded in the DCI format indicate the generation of an initializationvalue A (i.e., an initialization value for generating identicalreference signal sequences). Equation (4) may correspond to a situationwhere the 1-bit information additionally included in the DCI formatindicates the generation of initialization values B, which may beinitialization values for generating different reference signalsequences.

$\begin{matrix}{\mspace{79mu}{{c_{init} = {{\left( {\left\lfloor {n_{g}/2} \right\rfloor + 1} \right) \cdot \left( {{2N_{ID}^{cell}} + 1} \right) \cdot 2^{16}} + n_{SCID}}}\mspace{20mu}{{{where}\mspace{14mu} n_{SCID}} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu}{SCID}} = 0} \\1 & {{{if}\mspace{14mu}{SCID}} = 1}\end{matrix} \right.}}} & (3) \\{\mspace{79mu}{{c_{init} = {{\left( {\left\lfloor {n_{g}/2} \right\rfloor + 1} \right) \cdot \left( {{2N_{ID}^{cell}} + 1} \right) \cdot 2^{16}} + n_{A}}}{{{where}\mspace{14mu} n_{A}} = {n_{RNTI}\mspace{14mu}{or}\mspace{14mu}{n_{SCID}^{\prime}\left( {{regardless}\mspace{14mu}{of}\mspace{14mu}{whether}\mspace{14mu}{SCID}\mspace{14mu}{is}\mspace{14mu} 0\mspace{14mu}{or}\mspace{14mu} 1} \right)}}}}} & (4)\end{matrix}$

As compared with Equation (1), in Equation (3) and Equation (4), whenthe 1-bit information additionally included in the DCI format indicatesthe generation of the initialization value A or the first initializationvalue, which may be the initialization value for generating identicalreference signal sequences, a cell ID N_(ID) ^(cell) may become a commoncell ID or may be a cell ID of a cell or a point, to which a UE belongs,as in Equation (1). However, when the 1-bit information additionallyincluded in the DCI format indicates the generation of theinitialization values B or the second initialization values, which maybe the initialization values for generating different reference signalsequences, the cell ID N_(ID) ^(cell) may be the cell ID of the cell orthe point, to which the UE belongs, as in Equation (1).

Also, when the 1-bit information additionally included in the DCI formatindicates the generation of the initialization value A or the firstinitialization value (the initialization value for generating identicalreference signal sequences), a parameter n_(SCID) among parameters fordetermining an initialization value as defined by Equation (3) may havea value designated in a similar or the same manner as in Equation (1).When the 1-bit information additionally included in the DCI formatindicates the generation of the initialization values B or the secondinitialization values (the initialization values for generatingdifferent reference signal sequences), the parameter n_(SCID) may bereplaced by n_(A). Further, the value of n_(A) may be at least one of aUE-specific information, TP-specific information, n_(RNTI) representingthe value of RNTI, and n′_(SCID).

The n_(A) may signify a parameter, which may replace n_(SCID). However,when the n_(A) may have a similar or the same meaning and use as then_(SCID), aspects of the invention may not be limited to the notation ofthe scheme as described above. Accordingly, n_(A) may be denoted in ascheme other than the above scheme. For example, n_(SCID) may be used asan identical or corresponding parameter.

Similarly, in the method 2, initialization value generation informationmay include at least one of a cell ID N_(ID) ^(cell), a common cell ID,RNTI information, separately-defined UE-specific information,separately-defined TP-specific information, and a parameter related to aCSI-RS. When information that one or more UEs may not know exists amongthem, an eNodeB may transmit the relevant initialization valuegeneration information to one or more UEs through RRC signaling or thelike.

A method 3 for generating selection instruction information is describedin more detail below. The method 3 may be a mixed method in whichinstruction information related to a changed DM-RS may be configuredinstead of Table 2, and additional 1-bit information may be used.

The method 3 for generating selection instruction information may definechanged reference signal instruction information differently from thereference signal instruction information defined in Table 2, and may useexplicit 1-bit additional information for designating an initializationvalue, which may be identical, similar, corresponding or different,separately from the changed reference signal instruction information.

More specifically, a definition may be made of a table of 3-bitinformation on antenna port(s) and the number of layers, which may be atable matched to antenna port(s), a scrambling identity and the numberof layers that may be 3-bit information included in the existing DCIformat 2C as shown in Table 3 or Table 4 below, but which may notinclude a SCID. Further, an additional 1-bit for indicating aninitialization value A or initialization values B may be separatelydefined. Accordingly, in the method 3, the selection instructioninformation may become information having a total of 4 bits.

A conventional scheme as shown in Table 2 may enable MU-MIMO withrespect to a total of 4 layers by using an antenna port 7 and an antennaport 8 for the MU-MIMO and by applying SCID values of 0 and 1 to each ofthe antenna port 7 and the antenna port 8. However, in this situation,quasi-orthogonality, rather than normal orthogonality, may be ensuredbetween antenna ports when SCIDs are different from each other.

Accordingly, it may be more desirable to distinguish between layers ofMU-MIMO by using an antenna port without distinguishing between them byusing a SCID to ensure normal orthogonality. In this regard, Table 3 orTable 4 below may include a table of information on antenna port(s) andnumber of layers that may correspond to the method 3.

In a table such as Table 3 or Table 4 below, two additional antennaports may be used as well as the existing antenna port 7 and antennaport 8. The two additional ports may include, for example, antenna port9 and antenna port 10, or antenna port 11 and antenna port 13.Accordingly, in the method 3, Table 3 or Table 4 below may be used inplace of Table 2. Here, a SCID value is not separately included in DCI.

TABLE 3 One Codeword: Two Codewords: Codeword 0 enabled and Codeword 0enabled and Codeword 1 disabled Codeword 1 enabled Value Message ValueMessage 0 1 layer and port 7 0 2 layers and ports 7-8 1 1 layer and port8 1 2 layers and ports 9-10 2 1 layer and port 8 2 3 layers and ports7-9 3 1 layer and-port 10 3 4 layers and ports 7-10 4 2 layers and ports7-8 4 5 layers and ports 7-11 5 3 layers and ports 7-9 5 6 layers andports 7-12 6 4 layers and ports 7-10 6 7 layers and ports 7-13 7Reserved 7 8 layers and ports 7-14

TABLE 4 One Codeword: Two Codewords: Codeword 0 enabled and Codeword 0enabled and Codeword 1 disabled Codeword 1 enabled Value Message ValueMessage 0 1 layer and port 7 0 2 layers and ports 7-8 1 1 layer and port8 1 2 layers and ports 11 and 13 2 1 layer and port 11 2 3 layers andports 7-9 3 1 layer and port 13 3 4 layers and ports 7-10 4 2 layers andports 7-8 4 5 layers and ports 7-11 5 3 layers and ports 7-9 5 6 layersand ports 7-12 6 4 layers and ports 7-10 6 7 layers and ports 7-13 7Reserved 7 8 layers and ports 7-14

Accordingly, with respect to Table 3 or Table 4, the equation forcalculating an initialization value as defined by Equation (1) may bereplaced by Equation (5) or Equation (6) below. In each of Equation (5)and Equation (6) below, a formula expressing a reference signal sequencer(m) may be the same as that in Equation (1), and thus, a furtherdescription thereof will be omitted.

More specifically, when the 1-bit information, which may have a value of0 or, additionally included in the DCI format may indicate thegeneration of the initialization value A, which may be theinitialization value for generating identical reference signalsequences, the initialization value may be calculated by using Equation(5) below.c _(init)=(└n _(s)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +n _(A)where n _(A)=0  (5)

Further, when the 1-bit information additionally included in the DCIformat indicates the generation of the initialization values B, whichmay be the initialization values for generating different referencesignal sequences, the initialization values may be calculated by usingEquation (6) below.c _(init)=(└n _(g)/2┘+1)·(2N _(ID) ^(cell)+1)·2¹⁶ +n _(A)where n _(A) =n _(RNTI) or n′ _(SCID)  (6)

As compared with Equation (1), in Equation (5) and Equation (6), whenthe 1-bit information additionally included in the DCI format indicatesthe generation of the initialization value A, which may be theinitialization value for generating identical reference signalsequences, a cell ID N_(ID) ^(cell) may become a newly-defined commoncell ID or may be a cell ID of a cell or a point, to which a UE belongs,as in Equation (1).

However, when the 1-bit information additionally included in the DCIformat indicates the generation of the initialization values B, whichmay be the initialization values for generating different referencesignal sequences, a cell ID of a cell or a point, to which a UE belongsmay be used as the cell ID N_(ID) ^(cell), as in Equation (1).

Also, when the 1-bit information additionally included in the DCI formatindicates the generation of the initialization value A, n_(A) matched ton_(SCID) as shown in Equation (1) may have a default value, which mayhave a value of 0 as expressed in Equation (5), but the value of n_(A)is not limited thereto and may have other values. When the 1-bitinformation additionally included in the DCI format indicates thegeneration of the initialization values B, the value of n_(A) may becomea UE-specific value or a TP-specific value, which may include at leastone of RNTI information, separately-defined UE-specific information,separately-defined TP-specific information, and a parameter related to aCSI-RS.

In Equation (5) and Equation (6), n_(A) may signify a parameter that mayreplace n_(SCID). However, when n_(A) has a similar or the same meaningand use as the n_(SCID), aspects of the invention may not limited tonotation of the scheme as described above. For example, n_(A) may bedenoted in a scheme other than the above scheme, such that n_(SCID) maybe used as an identical or corresponding parameter.

Similarly, in the method 3, initialization value generation informationfor generating the reference signal sequence initialization value A orthe reference signal sequence initialization values B, which may respondto the initialization value selection instruction information, mayinclude at least one of a cell ID N_(ID) ^(cell), a common cell ID, RNTIinformation, separately-defined UE-specific information,separately-defined TP-specific information, and a parameter related to aCSI-RS. When information that one or more UEs may not know exists amongthem, an eNodeB may transmit the relevant initialization valuegeneration information to the respective UE or UEs through RRC signalingor the like.

A method 4 for generating selection instruction information is describedin more detail below. The method 4 may be a method in which new 4-bitinstruction information related to a DM-RS is defined instead of Table2.

The method 4 for generating selection instruction information may firstdefine new reference signal instruction information by using a total of4 bits differently from the reference signal instruction informationpreviously defined as in Table 2. Further, the method 4 may utilize theselection instruction information by using the new reference signalinstruction information.

More specifically, a new reference signal instruction information mayinclude at least one of a table of new information on one or moreantenna ports, a scrambling identity and the number of layers, which maybe a table matched to the one or more antenna ports, and a scramblingidentity and the number of layers that are 3-bit information included inthe existing DCI format 2C. The new reference signal information mayhave a total of 4 bits by adding 1 bit. Then, the defined table may beused to implicitly indicate the selection instruction information.

More specifically, at least one of a SCID value, which may be includedin 4-bit information on one or more antenna ports, a scramblingidentity, and the number of layers, as shown in Table 5 or Table 6below, may be used for indication. When SCID=0, an initialization valueA, which may be an initialization value for generating identicalreference signal sequences, may be generated. When SCID=1,initialization values B, which may be an initialization value forgenerating different reference signal sequences, may be generated. Incontrast, when SCID=1, the initialization value A may be generated. WhenSCID=0, the initialization values B may be generated.

TABLE 5 One Codeword: Two Codewords: Codeword 0 enabled; and Codeword 0enabled; and Codeword 1 disabled Codeword 1 enabled Value Message ValueMessage 0 1 layer, port 7 and SCID = 0 0 2 layers, ports 7-8 and SCID =0 1 1 layer, port 7 and SCID = 1 1 2 layers, ports 7-8 and SCID = 1 2 1layer, port 8 and SCID = 0 2 3 layers, ports 7-9 and SCID = 0 3 1 layer,port 8 and SCID = 1 3 4 layers, ports 7-10 and SCID = 0 4 2 layers,ports 7-8 and SCID = 0 4 5 layers, ports 7-11 and SCID = 0 5 3 layers,ports 7-9 and SCID = 0 5 6 layers, ports 7-12 and SCID = 0 6 4 layers,ports 7-10 and SCID = 0 6 7 layers, ports 7-13 and SCID = 0 7 1 layer,port 9 and SCID = 1 7 8 layers, ports 7-14 and SCID = 0 8 1 layer, port10 and SCID = 1 8 2 layers, ports 9-10 and SCID = 1 9 1 layer, port 11and SCID = 1 9 2 layers, ports 11 and 13, and SCID = 1 10 1 layer, port12 and SCID = 1 10 2 layers, ports 12 and 14, and SCID = 1 11 1 layer,port 13 and SCID = 1 11 Reserved 12 1 layer, port 14 and SCID = 1 12Reserved 13 Reserved 13 Reserved 14 Reserved 14 Reserved 15 Reserved 15Reserved or One Codeword: Two Codewords: Codeword 0 enabled and Codeword0 enabled and Codeword 1 disabled Codeword 1 enabled Value Message ValueMessage 0 1 layer, port 7 and SCID = 0 0 2 layers, ports 7-8 and SCID =0 1 1 layer, port 7 and SCID = 1 1 2 layers, ports 7-8 and SCID = 1 2 1layer, port 8 and SCID = 0 2 2 layers, ports 9-10 and SCID = 1 3 1layer, port 8 and SCID = 1 3 2 layers, ports 11 and 13, and SCID = 1 4 1layer, ports 9 and SCID = 1 4 2 layers, ports 12 and 14, and SCID = 1 51 layer, port 10 and SCID = 1 5 3 layers, ports 7-9 and SCID = 0 6 1layer, port 11 and SCID = 1 6 4 layers, ports 7-10 and SCID = 0 7 1layer, port 12 and SCID = 1 7 5 layers, ports 7-11 and SCID = 0 8 1layer, port 13 and SCID = 1 8 6 layers, ports 7-12 and SCID = 0 9 1layer, port 14 and SCID = 1 9 7 layers, ports 7-13 and SCID = 0 10 2layers, ports 7-8 and SCID = 0 10 8 layers, ports 7-14 and SCID = 0 11 3layers, ports 7-9 and SCID = 0 11 Reserved 12 4 layers, ports 7-10 andSCID = 0 12 Reserved 13 Reserved 13 Reserved 14 Reserved 14 Reserved 15Reserved 15 Reserved

TABLE 6 One Codeword: Two Codewords: Codeword 0 enabled and Codeword 0enabled and Codeword 1 disabled Codeword 1 enabled Value Message ValueMessage 0 1 layer, port 7 and SCID = 0 0 2 layers, ports 7-8 and SCID =0 1 1 layer, port 7 and SCID = 1 1 2 layers, ports 7-8 and SCID = 1 2 1layer, port 8 and SCID = 0 2 3 layers, ports 7-9 and SCID = 1 3 1 layer,port 8 and SCID = 1 3 4 layers, ports 7-10 and SCID = 1 4 2 layers,ports 7-8 and SCID = 1 4 5 layers, ports 7-11 and SCID = 1 5 3 layers,ports 7-9 and SCID = 1 5 6 layers, ports 7-12 and SCID = 1 6 4 layers,ports 7-10 and SCID = 1 6 7 layers, ports 7-13 and SCID = 1 7 1 layer,port 9 and SCID = 0 7 8 layers, ports 7-14 and SCID = 1 8 1 layer, port10 and SCID = 0 8 2 layers, ports 9-10 and SCID = 0 9 1 layer, port 11and SCID = 0 9 2 layers, ports 11 and 13, and SCID = 0 10 1 layer, port12 and SCID = 0 10 2 layers, ports 12 and 14, and SCID = 0 11 1 layer,port 13 and SCID = 0 11 Reserved 12 1 layer, port 14 and SCID = 0 12Reserved 13 Reserved 13 Reserved 14 Reserved 14 Reserved 15 Reserved 15Reserved or One Codeword: Two Codewords: Codeword 0 enabled and Codeword0 enabled and Codeword 1 disabled Codeword 1 enabled Value Message ValueMessage 0 1 layer, port 7 and SCID = 0 0 2 layers, ports 7-8 and SCID =0 1 1 layer, port 7 and SCID = 1 1 2 layers, ports 7-8 and SCID = 1 2 1layer, port 8 and SCID = 0 2 2 layers, ports 9-10 and SCID = 0 3 1layer, port 8 and SCID = 1 3 2 layers, ports 11 and 13, and SCID = 0 4 1layer, port 9 and SCID = 0 4 2 layers, ports 12 and 14, and SCID = 0 5 1layer, port 10 and SCID = 0 5 3 layers, ports 7-9 and SCID = 1 6 1layer, port 11 and SCID = 0 6 4 layers, ports 7-10 and SCID = 1 7 1layer, port 12 and SCID = 0 7 5 layers, ports 7-11 and SCID = 1 8 1layer, port 13 and SCID = 0 8 6 layers, ports 7-12 and SCID = 1 9 1layer, port 14 and SCID = 0 9 7 layers, ports 7-13 and SCID = 1 10 2layers, ports 7-8 and SCID = 1 10 8 layers, ports 7-14 and SCID = 1 11 3layers, port 7-9 and SCID = 1 11 Reserved 12 4 layers, ports 7-10 andSCID = 1 12 Reserved 13 Reserved 13 Reserved 14 Reserved 14 Reserved 15Reserved 15 Reserved

According to the method 4, the equation for calculating aninitialization value as defined by Equation (1) may be replaced byEquation (7) or Equation (8) below. In each of Equation (7) and Equation(8) below, a formula expressing a reference signal sequence r(m) may bethe same as that in Equation (1), and thus, a further descriptionthereof may be omitted.

$\begin{matrix}{{c_{init} = {{\left( {\left\lfloor {n_{g}/2} \right\rfloor + 1} \right) \cdot \left( {{2N_{ID}^{cell}} + 1} \right) \cdot 2^{16}} + n_{A}}}{{{where}\mspace{14mu} n_{A}} = \left\{ \begin{matrix}{n_{RNTI}\mspace{14mu}{or}\mspace{14mu} n_{SCID}^{\prime}} & {{{if}\mspace{14mu}{SCID}} = 0} \\{0\mspace{14mu}{or}\mspace{14mu} 1} & {{{if}\mspace{14mu}{SCID}} = 1}\end{matrix} \right.}} & (7) \\{{c_{init} = {{\left( {\left\lfloor {n_{g}/2} \right\rfloor + 1} \right) \cdot \left( {{2N_{ID}^{cell}} + 1} \right) \cdot 2^{16}} + n_{A}}}{{{where}\mspace{14mu} n_{A}} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu}{SCID}} = 0} \\{n_{RNTI}\mspace{14mu}{or}\mspace{14mu} n_{SCID}^{\prime}} & {{{if}\mspace{14mu}{SCID}} = 1}\end{matrix} \right.}} & (8)\end{matrix}$

More specifically, as compared with a situation in which a DCI format inan existing Release 10 (Rel-10), the method 1 may identically have 3bits as signaling bits. The method 2 and the method 3 may correspond tothe situation of adding 1 bit to the 3 bits. The method 4 may providemore flexibility in selecting an orthogonal port of a DM-RS by modifyingthe method 2 and the method 3.

Table 5 and Table 6 may include information associated with variousenvironments or situations. In these environments or situations, anorthogonal port of a DM-RS may be selected. According to aspects of theinvention, a total of 8 orthogonal ports may be used for MU-MIMO.However, the number of reserved rows may be increased to delete one ormore rows in Table 5 and Table 6 according to circumstances.

FIG. 4 is a flowchart illustrating a method for transmitting a referencesignal according to an exemplary embodiment of the present invention.

In generating a reference signal to be transmitted to an UE, in view ofa communication environment of a particular UE, a TP may select, as areference signal, at least one of an initialization value A (or a firstinitialization value) of a reference signal sequence identical for eachUE or TP, and an initialization value B (or a second initializationvalue) of a reference signal sequence different for one or more UEs orTPs. Further, the TP may generate a reference signal sequence based onthe relevant or selected initialization value (S420).

The eNodeB and/or the TP may generate selection instruction informationcorresponding to information on an initialization value selected fromamong the first initialization value and the second initializationvalue, and transmit the generated selection instruction information tothe UE in the form of a DCI format or the like (S425). As describedabove, the selection instruction information may be implicitly indicatedby at least one of the information on one or more antenna ports, ascrambling identity, and the number of layers that has 3 bits includedin the DCI format 2C, or by at least one of a newly defined 4-bitinformation on the one or more antenna ports, a scrambling identity, andthe number of layers. Further, the selection instruction information maybe separately generated by additionally using one or more explicitinstruction bits.

Also, the TP maps the reference signal sequence generated in operationS420 to an RE (S430), and generates a reference signal for transmittingto the relevant UE (S435).

Further, the UE receives, from the eNodeB and/or the TP, both theselection instruction information, which corresponds to information onan initialization value selected from among the first initializationvalue and the second initialization value, and the relevant referencesignal, which has been generated according to the selection instructioninformation (S440).

Also, the method of FIG. 4 may additionally include operation S410 andoperation S415 as an option. In operation S410, the TP transmitsinitialization value generation information to generate or change theinitialization value A and/or the initialization value B to the relevantUE. The initialization value generation information may include at leastone of a cell ID N_(ID) ^(cell), a common cell ID, RNTI information,separately-defined UE-specific information, separately-definedTP-specific information, and a parameter related to a CSI-RS. However,aspects of the invention are not limited thereto.

When the TP transmits the initialization value generation information tothe UE, high layer signaling, such as RRC, may be used. However, aspectsof the invention are not limited thereto.

The UE may receive the initialization value generation informationtransmitted by the TP (S415).

Further, the UE may be aware of at least one of the RNTI information, acell ID of a cell or a point to which the UE belongs, and informationrelated to a CSI-RS, among the initialization value generationinformation necessary to generate or change the initialization value Aand/or the initialization value B. Accordingly, the TP may not have toseparately transmit this initialization value generation information tothe UE. In such a situation, operation S410 and operation S415 may beomitted.

A determination to which information is to be used among theinitialization value generation information, may be made according to anenvironment of a communication system. The environment of thecommunication system may include at least one of the types of CoMPscenario, a CoMP scheme, and a determination of whether MU-MIMO issupported.

The UE which receives, from the TP, the selection instructioninformation of one of the initialization value A of identical referencesignal sequences or the initialization value B of different referencesignal sequence, generates a reference signal in a scheme indicated bythe selection instruction information by using the initialization valuegeneration information that the UE has received or is already aware of(S445). The initialization value generation information may be receivedin advance by the UE.

Further, the UE estimates a channel by comparing the reference signalgenerated in step S445 with the reference signal received from the TP instep S440 (S450).

Therefore, in the communication system supporting CoMP and/or MU-MIMOand the like, the TP may transmit, to the UE, the reference signalidentical, similar, corresponding, or different for one or more UEs orTPs according to the environment of the UE, and may enable the UE toestimate a channel.

FIG. 5 is a flowchart showing a method for transmitting a referencesignal by a TP according to an exemplary embodiment of the presentinvention.

In FIG. 5, a subject that transmits a reference signal may be referredto as a TP. A subject that transmits instruction information related tothe generation of a reference signal may be referred to as an eNodeBand/or a TP, which receives the instruction information from the eNodeB.Accordingly, a method and an apparatus in the eNodeB may bedistinguished from those in the TP. However, the eNodeB may alsocorrespond to a TP. Accordingly, a method and an apparatus in the eNodeBmay be integrated into those in the TP.

In generating a reference signal to be transmitted to one or more UEs,in view of a communication environment of a particular UE, the TP mayselect one of an initialization value A of a reference signal sequenceidentical for one or more UEs or TPs and an initialization value B of areference signal sequence different for each UE or TP, and generates areference signal sequence based on the relevant initialization value(S510).

Further, the TP generates selection instruction informationcorresponding to information on an initialization value selected fromamong the first initialization value and the second initializationvalue, and transmits the generated selection instruction information tothe UE in the form of a DCI format or the like (S520).

The selection instruction information according to an exemplaryembodiment of the present invention may be implicitly indicated by atleast one of the information on one or more antenna ports, a scramblingidentity, and the number of layers that has 3 bits included in theexisting DCI format 2C, or by at least one of the newly defined 4-bitinformation on one or more antenna ports, a scrambling identity, and thenumber of layers. Otherwise, a DCI format may include a 1-bitinstruction bit, which may be separately defined together with theinstruction information related to the DM-RS as described above, and theselection instruction information may be explicitly indicated by the1-bit instruction bit.

In operation S530, the TP maps the reference signal sequence generatedin step S520 to an RE. In operation S540, the TP generates a referencesignal and transmits the generated reference signal to the relevant UE.

Also, before performing step S510, the method may additionally includestep S505 in which the TP generates initialization value generationinformation to generate or change the first initialization value or thesecond initialization value, and transmits the generated initializationvalue generation information to the relevant UE. The initializationvalue generation information may include at least one of a cell IDN_(ID) ^(cell), a common cell ID, RNTI information, separately-definedUE-specific information, separately-defined TP-specific information, anda parameter related to a CSI-RS. However, aspects of the invention arenot limited thereto.

When the TP transmits the initialization value generation information tothe UE, high layer signaling such as RRC may be used. However, aspectsof the invention are not limited thereto.

Further, the UE may know or be aware of at least one of the RNTIinformation, a cell ID of a cell or a point to which the UE belongs, andinformation related to a CSI-RS, among the initialization valuegeneration information that may be used to generate or change theinitialization value A and/or the initialization value B. Accordingly,the TP may not separately transmit the initialization value generationinformation to the UE. In such a situation or environment, step S505 maybe omitted.

FIG. 6 is a flowchart showing a method for estimating a channel by amobile station according to an exemplary embodiment of the presentinvention.

In operation S610, a UE receives selection instruction information on aninitialization value of a reference signal sequence, which may betransmitted by a TP, such as an eNodeB.

The selection instruction information may refer to informationindicating that an initialization value of a sequence for a referencesignal, which is to be transmitted by the TP, is either aninitialization value A of a reference signal sequence identical for oneor more UEs or TPs, or an initialization value B of a reference signalsequence different for one or more UEs or TPs. The selection instructioninformation may be transmitted in the DCI format.

As described above, the selection instruction information may beimplicitly indicated by at least one of the information on one or moreantenna ports, a scrambling identity, and the number of layers that has3 bits included in the DCI format 2C, or by at least one of the newlydefined 4-bit information on one or more antenna ports, a scramblingidentity, and the number of layers. Otherwise, the selection instructioninformation may separately be generated by additionally using oneexplicit instruction bit. Also, the UE receives a reference signal thatthe TP generates and transmits according to the selection instructioninformation (S620).

In operation S630, the UE identifies initialization value generationinformation for generating a reference signal sequence. In operationS640, the UE generates a reference signal in a scheme indicated by theselection instruction information by using the identified initializationvalue generation information.

In operation S650, the UE estimates a channel by comparing the referencesignal generated in step S640 with the reference signal received fromthe TP in operation S620.

Further, the method may additionally include operation S605 in which theUE receives initialization value generation information used to generateor change the first initialization value or the second initializationvalues from the TP through RRC or the like. The initialization valuegeneration information may include at least one of a cell ID, a commoncell ID, RNTI information, separately-defined UE-specific information,separately-defined TP-specific information, and a parameter related to aCSI-RS. However, aspects of the invention are not limited thereto.

Further, the UE may know or be aware of at least one of the RNTIinformation, a cell ID of a cell or a point to which the UE belongs, andinformation related to a CSI-RS, among the initialization valuegeneration information used to generate or change the firstinitialization value or the second initialization value. Accordingly,the TP may not separately transmit this initialization value generationinformation to the UE. In such a situation, operation S605 may beomitted.

FIG. 7 is a block diagram illustrating a configuration of an apparatusto generate and transmit a reference signal and information related tothe generation of the reference signal according to an exemplaryembodiment of the present invention.

The apparatus to generate and transmit a reference signal andinformation related to the generation of the reference signal accordingto exemplary embodiments of the present invention may be implementedwithin the eNodeB and/or the TP or as a part of the eNodeB and/or theTP. However, aspects of the invention are not limited thereto.

The apparatus 700 to generate and transmit a reference signal andinformation related to the generation of the reference signal accordingto exemplary embodiments of the present invention includes: a selectioninstruction information generator 710 to generate selection instructioninformation on an initialization value of a reference signal sequence; areference signal generator 720 to generate a downlink reference signalaccording to a determined scheme; and a transmitter 730 to transmit atleast one of the selection instruction information and the generatedreference signal to one or more UEs. Selectively, the apparatus 700 mayadditionally include an initialization value generation informationprocessor 740 to generate initialization value generation informationused to change or generate the initialization value of the referencesignal sequence and transmit the generated initialization valuegeneration information to one or more UEs.

In generating a reference signal to be transmitted to one or more UEs,in view of a communication environment of a particular UE, the selectioninstruction information generator 710 may generate selection instructioninformation indicating one of an initialization value A (or a firstinitialization value) of a reference signal sequence identical, similar,or corresponding for each UE or TP, or one or more UEs or TPs, and aninitialization value B (or a second initialization value) of a referencesignal sequence different for each UE or TP, or one or more UEs or TPs.

As described above in relation to Equation (2), Equation (3), Equation(4), Equation (5), Equation (6), Equation (7), and Equation (8), theselection instruction information may be implicitly indicated by atleast one of the information on one or more antenna ports, a scramblingidentity, and the number of layers that has 3 bits included in the DCIformat 2C, or by at least one of the newly-defined 4-bit information onone or more antenna ports, a scrambling identity, and the number oflayers. Otherwise, a DCI format may separately include a 1-bitinstruction bit, and the selection instruction information may beexplicitly indicated by the 1-bit instruction bit.

The generated selection instruction information may be transmitted tothe UE by the transmitter 730 in the form of a DCI format or the like.

The reference signal generator 720 may generate a downlink referencesignal in a scheme matched or corresponding to the selection instructioninformation transmitted to the UE. Further, according to theinitialization value A or the initialization values B, reference signalsidentical, similar, corresponding, or different according to the UEs orTPs may be generated.

Also, the initialization value generation information processor 740 maygenerate initialization value generation information that may be used togenerate or change the first initialization value or the secondinitialization value, which may include at least one of a cell ID, acommon cell ID, RNTI information, separately-defined UE-specificinformation, separately-defined TP-specific information and a parameterrelated to a CSI-RS. Further, the initialization value generationinformation processor 740 may transmit the generated initializationvalue generation information to the UE through RRC signaling by usingthe transmitter.

FIG. 8 is a block diagram illustrating a configuration of an apparatusto estimate a channel according to an exemplary embodiment of thepresent invention.

The apparatus to estimate a channel according to an exemplary embodimentof the present invention may be implemented within the UE or as a partof the UE. However, aspects of the invention are not limited thereto.

The apparatus 800 to estimate a channel according to an exemplaryembodiment of the present invention may include: a reference signalreceiver 810 to receive a reference signal from the TP; a selectioninstruction information receiver 820 to receive, from the TP, selectioninstruction information corresponding to information on aninitialization value of a reference signal; an initialization valuegeneration information identifier 830 to identify initialization valuegeneration information used to generate or change the initializationvalue used to generate the reference signal; a reference signalgenerator 840 to generate a reference signal based on the receivedselection instruction information and the identified initializationvalue generation information; and a channel estimator 850 to estimate achannel state by comparing the generated reference signal with thereceived reference signal. Also, selectively, the apparatus 800 mayadditionally include an initialization value generation informationreceiver 860 to receive, from the TP, initialization value generationinformation used to change or generate an initialization value of areference signal sequence.

The reference signal receiver 810 may receive a reference signaltransmitted by the TP. Further, the received reference signal may be areference signal, which may be generated according to selectioninstruction information and transmitted. The selection instructioninformation may indicate that an initialization value of a sequence forthe reference signal transmitted by the TP may be an initializationvalue A (or a first initialization value) of a reference signalsequence, or an initialization value B (or a second initializationvalue) of a reference signal sequence. The initialization value A of thereference signal sequence may be identical, similar, or corresponding toeach UE or TP (or one or more UEs or TPs). The initialization value B ofthe reference signal sequence may be different for each UE or TP (or oneor more UEs or TPs).

The selection instruction information may refer to information, whichmay be explicitly or implicitly known by the UE. The TP may generate theselection instruction information according to the scheme as shown inEquation (2), Equation (3), Equation (4), Equation (5), Equation (6),Equation (7), and Equation (8). Further, the TP may transmit thegenerated selection instruction information to the UE. Further, theselection instruction information receiver 820 may receive the selectioninstruction information.

The initialization value generation information identifier 830 mayidentify initialization value generation information that may be used togenerate or change an initialization value used when the UE generates areference signal. The initialization value generation information mayinclude at least one of a cell ID of a cell or a point to which the UEmay belong, a common cell ID, RNTI information, separately-definedUE-specific information, separately-defined TP-specific information, anda parameter related to a CSI-RS. However, aspects of the invention arenot limited thereto. Also, the UE may know or be aware of theinitialization value generation information. However, according tocircumstances, the initialization value generation information receiver860 may receive the initialization value generation information from theTP, and the UE may detect it.

The reference signal generator 840 may generate a reference signal in ascheme matched or corresponding to the received selection instructioninformation by using the identified or received initialization valuegeneration information.

The channel estimator 850 may compare the reference signal generated bythe reference signal generator 840 with the reference signal received bythe reference signal receiver 810, and may estimate a channel state as aresult of the comparison.

According to exemplary embodiments of the present invention as describedabove, when generating a downlink reference signal to be transmitted toone or more UEs in the communication system supporting CoMP and/orMU-MIMO and the like, according to an environment of each UE, aninitialization value A of a reference signal sequence identical for eachUE or TP and an initialization value B of a reference signal sequencedifferent for each UE or TP may be selected, and a reference signal maybe generated based on the selected initialization value. Accordingly,aspects of the invention may allow one or more UEs to estimate achannel.

Also, the type of reference signal initialization value A or referencesignal initialization value B may dynamically be indicated to one ormore UEs. Accordingly, exemplary embodiments of the present inventionmay provide such an effect that the orthogonality of downlink referencesignals and/or the pseudo orthogonality thereof can be maintained orimproved in a communication environment of CoMP or MIMO.

Although the components of an apparatus according to exemplaryembodiments of the present invention are coupled as a single unit orcoupled to be operated as a single unit, aspects of the invention arenot limited thereto. For example, one or more components among thecomponents may be selectively coupled to be operated as one or moreunits. Also, although one or more of the components may be implementedas an independent hardware, some or all of the components may beselectively combined with each other, so that they may be implemented asa computer program having one or more program modules to perform some orall of the operations combined in one or more hardwares. Codes and codesegments forming the computer program may be conceived by an ordinarilyskilled person in the relevant technical field. Such a computer programmay implement the exemplary embodiments of the present invention bybeing stored in a non-transitory computer-readable medium, and beingread and executed by the computer with a processor. Storage mediums tostore computer program may include a magnetic recording medium, anoptical recording medium, a carrier wave medium, and the like.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for transmitting a reference signal,comprising: configuring first initialization value generationinformation associated with a first value of scrambling code identity(SCID) (n_(SCID)) information and second initialization value generationinformation associated with a second value of the SCID (n_(SCID))information, wherein the first initialization value generationinformation and the second initialization value generation informationcomprise respective cell identity (cell ID) information, wherein therespective cell ID information is selected based on the SCID (n_(SCID))information; transmitting, to a user equipment (UE), the firstinitialization value generation information and the secondinitialization value generation information through a higher layersignaling; transmitting, to the UE, the SCID (n_(SCID)) information asselection indication information; generating a reference signal for theUE based on one of a first initialization value and a secondinitialization value selected by the SCID (n_(SCID)) information, thefirst initialization value being determined based on the firstinitialization value generation information and the secondinitialization value being determined based on the second initializationvalue generation information; and transmitting the generated referencesignal to the UE.
 2. The method of claim 1, wherein the higher layersignaling corresponds to a radio resource control (RRC) signaling. 3.The method of claim 1, wherein the SCID (n_(SCID)) information isincluded in downlink control information (DCI).
 4. The method of claim1, wherein the SCID (n_(SCID)) information corresponds to a SCID valueincluded in 3-bit information representing antenna port(s), a scramblingidentity, and a number of layers.
 5. A method of operating a userequipment (UE), comprising: receiving, from a base station (BS), a firstreference signal; receiving first initialization value generationinformation associated with a first value of scrambling code identity(SCID) (n_(SCID)) information and second initialization value generationinformation associated with a second value of the SCID (n_(SCID))information through a higher layer signaling, wherein the firstinitialization value generation information and the secondinitialization value generation information comprise respective cellidentity (cell ID) information, wherein the respective cell IDinformation is selected based on the SCID (n_(SCID)) information;receiving the SCID (n_(SCID)) information as selection indicationinformation; generating a second reference signal based on one of afirst initialization value and a second initialization value indicatedby the SCID (n_(SCID)) information, the first initialization value beingdetermined based on the first initialization value generationinformation and the second initialization value being determined basedon the second initialization value generation information; andestimating a channel state by comparing the second reference signal withthe first reference signal.
 6. The method of claim 5, wherein the higherlayer signaling corresponds to a radio resource control (RRC) signaling.7. The method of claim 5, wherein the SCID (n_(SCID)) information isincluded in downlink control information (DCI).
 8. The method of claim5, wherein the SCID (n_(SCID)) information corresponds to a SCID valueincluded in 3-bit information representing antenna port(s), a scramblingidentity, and a number of layers.
 9. A user equipment (UE) configuredfor receiving a reference signal, comprising: one or more receivers; aprocessor coupled to the one or more receivers, wherein the processor isconfigured to cause the UE to: receive a first reference signalgenerated for the UE; receive first initialization value generationinformation associated with a first value of scrambling code identity(SCID) (n_(SCID)) information and second initialization value generationinformation associated with a second value of the SCID (n_(SCID))information through a higher layer signaling, wherein the firstinitialization value generation information and the secondinitialization value generation information comprise respective cellidentity (cell ID) information, wherein the respective cell IDinformation is selected based on the SCID (n_(SCID)) information;receive the SCID (n_(SCID)) information as selection indicationinformation; generate a second reference signal based on one of a firstinitialization value and a second initialization value indicated by theSCID (n_(SCID)) information, the first initialization value beingdetermined based on the first initialization value generationinformation and the second initialization value being determined basedon the second initialization value generation information; and estimatea channel state by comparing the second reference signal with the firstreference signal.
 10. The UE of claim 9, wherein the higher layersignaling corresponds to a radio resource control (RRC) signaling. 11.The UE of claim 9, wherein the SCID (n_(SCID)) information is includedin downlink control information (DCI).
 12. The UE of claim 9, whereinthe SCID (n_(SCID)) information corresponds to a SCID value included in3-bit information representing antenna port(s), a scrambling identity,and a number of layers.
 13. The method of claim 1, wherein at least oneof the first initialization value generation information and the secondinitialization value generation information comprise a parameter relatedto a channel state information reference signal (CSI-RS).
 14. The methodof claim 3, wherein the DCI is in DCI format 2C.
 15. The method of claim5, wherein at least one of the first initialization value generationinformation and the second initialization value generation informationcomprise a parameter related to a channel state information referencesignal (CSI-RS).
 16. The method of claim 7, wherein the DCI is in DCIformat 2C.
 17. The UE of claim 9, wherein at least one of the firstinitialization value generation information and the secondinitialization value generation information comprise a parameter relatedto a channel state information reference signal (CSI-RS).
 18. The UE ofclaim 11, wherein the DCI is in DCI format 2C.